Starting from this commit :
LUCENE-5666: get solr started
git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene5666@1594254 13f79535-47bb-0310-9956-ffa450edef68
It is not possible to use Term Enum as a faceting method, for numeric and single valued fields ( org.apache.solr.request.SimpleFacets ) .
We personally verified that there are use cases when this is bringing a quite big performance regression ( even with DocValues enabled) .
In the mailing list from time to time people complain about a regression happening with the term enum method, but actually it is more likely to be the automatic forcing of FCS.
Forcing FCS in co-op with the famous regression that happened in SOLR-8096 could be confused as a term Enum regression.